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From: Nikolay Aleksandrov <nikolay@cumulusnetworks•com>
To: Roopa Prabhu <roopa@cumulusnetworks•com>, davem@davemloft•net
Cc: stephen@networkplumber•org, netdev@vger•kernel.org
Subject: Re: [PATCH net-next v2] bridge: set is_local and is_static before fdb entry is added to the fdb hashtable
Date: Tue, 27 Oct 2015 14:31:48 +0100	[thread overview]
Message-ID: <562F7CC4.6040604@cumulusnetworks.com> (raw)
In-Reply-To: <1445947922-12236-1-git-send-email-roopa@cumulusnetworks.com>

On 10/27/2015 01:12 PM, Roopa Prabhu wrote:
> From: Roopa Prabhu <roopa@cumulusnetworks•com>
> 
> Problem Description:
> We can add fdbs pointing to the bridge with NULL ->dst but that has a
> few race conditions because br_fdb_insert() is used which first creates
> the fdb and then, after the fdb has been published/linked, sets
> "is_local" to 1 and in that time frame if a packet arrives for that fdb
> it may see it as non-local and either do a NULL ptr dereference in
> br_forward() or attach the fdb to the port where it arrived, and later
> br_fdb_insert() will make it local thus getting a wrong fdb entry.
> Call chain br_handle_frame_finish() -> br_forward():
> But in br_handle_frame_finish() in order to call br_forward() the dst
> should not be local i.e. skb != NULL, whenever the dst is
> found to be local skb is set to NULL so we can't forward it,
> and here comes the problem since it's running only
> with RCU when forwarding packets it can see the entry before "is_local"
> is set to 1 and actually try to dereference NULL.
> The main issue is that if someone sends a packet to the switch while
> it's adding the entry which points to the bridge device, it may
> dereference NULL ptr. This is needed now after we can add fdbs
> pointing to the bridge.  This poses a problem for
> br_fdb_update() as well, while someone's adding a bridge fdb, but
> before it has is_local == 1, it might get moved to a port if it comes
> as a source mac and then it may get its "is_local" set to 1
> 
> This patch changes fdb_create to take is_local and is_static as
> arguments to set these values in the fdb entry before it is added to the
> hash. Also adds null check for port in br_forward.
> 
> Reported-by: Nikolay Aleksandrov <nikolay@cumulusnetworks•com>
> Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks•com>
> ---
> v2 - fix compile error reported by kbuild test robot.
>      Accidently i had posted an older version of the patch
> 

Thanks for fixing this,

Fixes: 3741873b4f73 ("bridge: allow adding of fdb entries pointing to the bridge device")
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks•com>

next prev parent reply	other threads:[~2015-10-27 13:39 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-27 12:12 [PATCH net-next v2] bridge: set is_local and is_static before fdb entry is added to the fdb hashtable Roopa Prabhu
2015-10-27 13:31 ` Nikolay Aleksandrov [this message]
2015-10-27 14:02   ` David Miller
2015-10-27 14:55     ` roopa

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